Cottoneeand its evolution Whimsicottlook too cute to be really useful at first glance, but they've definitely got their advantages in battle. As you know, Leech Seed is the most formidable Grass-type move in existence.Once you've seeded your opponent,Leech Seed takes 1/16ofits HP each turn, and gives all the HP it drained from your opponent to your Pokemon. 1/16 doesn't seem like much, but it adds up quickly, since once you've seeded the Pokemon, it drains HP each turn like a poison, without taking up additional turns, and you get the full amount restored to the Pokemon who used Leech Seed, or if you switch out, to whatever Pokemon takes its place. If you add a Big Root hold item to that equation, you get the full HP of your opponent plus 30%.

Cottonee and Whimsicott'sPrankster ability gives priority to non-damaging moves, and Leech Seed is included in this since it doesn't do damage when the opponent is seeded initially. Add to thatWhimsicott's already impressivespeed stat, andit has the potential to seriously disrupt your opponent's plans.Prankster coupled with Whimsicott's speed also go hand in hand for any other non-damaging strategies you can think of, like Substitute, Encore and Taunt.